Dark matter as integration constant in Horava-Lifshitz gravity

In the non-relativistic theory of gravitation recently proposed by Horava, the Hamiltonian constraint is not a local equation satisfied at each spatial point but an equation integrated over a whole space. The global Hamiltonian constraint is less restrictive than its local version, and allows a richer set of solutions than in general relativity. We show that a component which behaves like pressureless dust emerges as an "integration constant" of dynamical equations and momentum constraint equations. Consequently, classical solutions to the infrared limit of Horava-Lifshitz gravity can mimic general relativity plus cold dark matter.Comment: 16 pages; (non-)conservation equation for "dark matter" added (v2); note added to comment on some recent preprints (v3); version accepted for publication in PRD (v4

NRL Dutch national programme studies VI/VII (2000) on bacteriological detection of Salmonella and pilot collaborative study I/II on detection of Campylobacter

In 2000, two bacteriological collaborative studies were organized by the Dutch National Reference Laboratory (NRL) for Salmonella among 23 laboratories participating in the Dutch national programme for control of Salmonella in the poultry sector. The main objective of these studies was to test the capacity of these laboratories to detect Salmonella in the presence of competitive micro-organisms. Reference capsules containing sublethally injured Salmonella Typhimurium had to be tested for the presence of Salmonella with and without the addition of chicken faeces. The method used in the studies was prescribed by the Product Boards for Livestock, Meat and Eggs. In this method the semi-solid medium MSRV had to be used as the selective enrichment medium. Depending on the results from previous collaborative studies, laboratories had to test 50 or 15 capsules. Only in the first study (study VI) one laboratory tested 50 capsules and this laboratory detected Salmonella from all Salmonella positive capsules. In this study VI 22 (of the 23) and in study VII 18 (of the 21) participating laboratores isolated Salmonella from all 10 Salmonella positive capsules. Additionally two pilot bacteriological collaborative studies on the detection methods of Campylobacter were organized. The main goal of these two pilot studies was that the participating laboratories could get experience with the detection of Campylobacter.In 2000 werden er twee bacteriologische ringonderzoeken voor de detectie van Salmonella in aanwezigheid van stoorflora georganiseerd door het Nationaal Referentie Laboratorium (NRL) voor Salmonella, waaraan werd deelgenomen door 23 laboratoria die betrokken zijn bij het plan van aanpak Salmonella en Campylobacter in de pluimveehouderij. Het belangrijkste doel van deze ringonderzoeken was te testen of de deelnemende laboratoria in staat waren om Salmonella te detecteren in aanwezigheid van stoorflora. Daarvoor werden referentiematerialen met Salmonella Typhimurium gebruikt die dienden te worden onderzocht met en zonder toevoeging van kippenfeces. De gebruikte methode was voorgeschreven door de Productschappen Vee, Vlees en Eieren (PVE). In deze methode moet het semi-solid medium MSRV gebruikt worden als selectief ophopingsmedium. Naar aanleiding van de resultaten die de deelnemende laboratoria in eerdere ringonderzoeken behaalden moesten 50 of 15 capsules onderzocht worden. Alleen in ringonderzoek VI (roz VI) moesten door een laboratorium 50 capsules worden onderzocht en dit laboratorium isoleerde Salmonella uit alle Salmonella positieve monsters. In roz VI isoleerden 22 (van de 23) en in roz VII 18 (van de 21) deelnemende laboratoria Salmonella uit alle 10 Salmonella positieve capsules. Daarnaast werden er voor de eerste keer pilot ringonderzoeken voor de bacteriologische detectie van Campylobacter georganiseerd met als doel laboratoria ervaring te laten opdoen met de detectie van Campylobacter

Spacetime Foam, Holographic Principle, and Black Hole Quantum Computers

Spacetime foam, also known as quantum foam, has its origin in quantum fluctuations of spacetime. Arguably it is the source of the holographic principle, which severely limits how densely information can be packed in space. Its physics is also intimately linked to that of black holes and computation. In particular, the same underlying physics is shown to govern the computational power of black hole quantum computers.Comment: 8 pages, LaTeX; Talk given by Jack Ng, in celebration of Paul Frampton's 60th birthday, at the Coral Gables Conference (in Fort Lauderdale, Florida on December 17, 2003). To appear in the Proceedings of the 2003 Coral Gables Conferenc

Quantum Entanglement and Communication Complexity

We consider a variation of the multi-party communication complexity scenario where the parties are supplied with an extra resource: particles in an entangled quantum state. We show that, although a prior quantum entanglement cannot be used to simulate a communication channel, it can reduce the communication complexity of functions in some cases. Specifically, we show that, for a particular function among three parties (each of which possesses part of the function's input), a prior quantum entanglement enables them to learn the value of the function with only three bits of communication occurring among the parties, whereas, without quantum entanglement, four bits of communication are necessary. We also show that, for a particular two-party probabilistic communication complexity problem, quantum entanglement results in less communication than is required with only classical random correlations (instead of quantum entanglement). These results are a noteworthy contrast to the well-known fact that quantum entanglement cannot be used to actually simulate communication among remote parties.Comment: 10 pages, latex, no figure

Bigravity and Lorentz-violating Massive Gravity

Bigravity is a natural arena where a non-linear theory of massive gravity can be formulated. If the interaction between the metrics $f$ and $g$ is non-derivative, spherically symmetric exact solutions can be found. At large distances from the origin, these are generically Lorentz-breaking bi-flat solutions (provided that the corresponding vacuum energies are adjusted appropriately). The spectrum of linearized perturbations around such backgrounds contains a massless as well as a massive graviton, with {\em two} physical polarizations each. There are no propagating vectors or scalars, and the theory is ghost free (as happens with certain massive gravities with explicit breaking of Lorentz invariance). At the linearized level, corrections to GR are proportional to the square of the graviton mass, and so there is no vDVZ discontinuity. Surprisingly, the solution of linear theory for a static spherically symmetric source does {\em not} agree with the linearization of any of the known exact solutions. The latter coincide with the standard Schwarzschild-(A)dS solutions of General Relativity, with no corrections at all. Another interesting class of solutions is obtained where $f$ and $g$ are proportional to each other. The case of bi-de Sitter solutions is analyzed in some detail.Comment: 25 pages. v3 Typos corrected, references added. v4 Introduction extende

Spontaneous Lorentz Breaking and Massive Gravity

We study a theory where the presence of an extra spin-two field coupled to gravity gives rise to a phase with spontaneously broken Lorentz symmetry. In this phase gravity is massive, and the Weak Equivalence Principle is respected. The newtonian potentials are in general modified, but we identify an non-perturbative symmetry that protects them. The gravitational waves sector has a rich phenomenology: sources emit a combination of massless and massive gravitons that propagate with distinct velocities and also oscillate. Since their velocities differ from the speed of light, the time of flight difference between gravitons and photons from a common source could be measured.Comment: 4 page

Modeling of time-resolved laser-induced incandescence transients for particle sizing in high-pressure spray combustion environments: a comparative study

In this study experimental single-pulse, time-resolved laser-induced incandescence (TIRE-LII) signal intensity profiles acquired during transient Diesel combustion events at high pressure were processed. Experiments were performed between 0.6 and 7MPa using a high-temperature high-pressure constant volume cell and a heavy-duty Diesel engine, respectively. Three currently available LII sub-model functions were investigated in their performance for extracting ensemble mean soot particle diameters using a least-squares fitting routine, and a "quick-fit” interpolation approach, respectively. In the calculations a particle size distribution as well as the temporal and spatial intensity profile of the heating laser was taken into account. For the poorly characterized sample environments of this work, some deficiencies in these state-of-the-art data evaluation procedures were revealed. Depending on the implemented model function, significant differences in the extracted particle size parameters are apparent. We also observe that the obtained "best-fit” size parameters in the fitting procedure are biased by the choice of their respective "first-guess” initial values. This behavior may be caused by the smooth temporal profile of the LII cooling curve, giving rise to shallow local minima on the multi-parameter least squares residuals, surface sampled during the regression analysis procedure. Knowledge of the gas phase temperature of the probed medium is considered important for obtaining unbiased size parameter information from TIRE-LII measurement